Synthesis of 3-iodothiophenes via iodocyclization of (Z)-thiobutenynes

A simple synthesis of 3-iodothiophenes was demonstrated using a wide range of (Z)-thioenynes. The key step in the iodocyclofunctionalization was the selective reduction of the triple bond in (Z)-thioenynes by the addition of iodine as an electrophilic agent. The 3-iodothiophenes were obtained in good to excellent yields of 61–92%. The 3-iodothiophenes were used as substrates in Sonogashira cross-coupling reactions to obtain thiophene acetylenes.     

Collisional effects in the tokamap

Plasmas confined in tokamaks with non-symmetric perturbations are surrounded by a chaotic layer of magnetic field lines that guide charged particles to the tokamak wall. We use an analytical two-dimensional symplectic mapping to study the resulting fractal patterns of field line escape. However, particles may experience several collisions before escaping toward the tokamaks wall. We add a random collisional term to the field line mapping to investigate how the particle collisions modify their escape patterns.     

Red long-lasting luminescence in clinoenstatite

A long-lasting phosphor Ca_0.2Zn_0.9Mg_0.9Si₂O₆:Eu²⁺, Dy³⁺, Mn²⁺ was prepared by a sol-gel method. Nanoparticles crystallizing in a clinoenstatite structure were obtained. Long persistent phosphorescence in the red has been observed with persistence time over one hour at 680 nm and was attributed to Mn²⁺ emission. The persistent luminescence is suggested to involve Eu²⁺ as a sensitizer, Dy³⁺ or Dy³⁺-related defect as a trap center and Mn²⁺ as the luminescent center. However, the details of the mechanism are still under further investigation.     

Importance sampling of rare events in chaotic systems

The European Physical Journal B - A way to make financial models effective is by letting them to represent the so called “fat tails”, i.e., extreme changes in stock prices that are...     

About pycnometric density measurements

Pycnometric density is at the moment the closest approximation of true density calculated from the molecular weight and crystalline lattice of the product. It is determined by using helium pycnometers that offer the advantage of being easy-to-use and rapid, especially fully automated apparatus. If the accuracy and the reproducibility of the technique are sufficient to reveal minute variations, this data is of interest for characterisation of crystalline structures (polymorphs, pseudopolymorphs, amorphous state), detection of defects, pores or impurities, and possible changes in crystal density during compaction. The aim of this article is to investigate on the confidence that can be expected when measuring density with an AccuPyc 1330 pycnometer. The experiments carried out on glass beads, quartz and mannitol have shown that operating parameters can affect the accuracy of pycnometric density to the nearest 0.01 g cm(-3). If measurements are performed in optimal conditions, 0.02% accuracy can be obtained, otherwise it can fail to 0.1% or less, depending on the material and the variations in the standard volume.     

Tokamak magnetic field lines described by simple maps

The magnetic field line structure in a tokamak can be obtained by direct numerical integration of the field line equations. However, this is a lengthy procedure and the analysis of the solution may be very time-consuming. Otherwise we can use simple two-dimensional, area-preserving maps, obtained either by approximations of the magnetic field line equations, or from dynamical considerations. These maps can be quickly iterated, furnishing solutions that mirror the ones obtained from direct numerical integration, and which are useful when long-term studies of field line behavior are necessary (e.g. in diffusion calculations). In this work we focus on a set of simple tokamak maps for which these advantages are specially pronounced.     

Efficient laser action of Yb:LSO and Yb:YSO oxyorthosilicates crystals under high-power diode-pumping

We report here on the efficient laser action of a new Yb-doped crystal Yb³⁺:Lu₂SiO₅ (Yb:LSO) under high power diode-pumping (15 W). Its performances were compared to another Yb-doped crystal belonging to the oxyorthosilicate family: the Yb:YSO. For both crystals, more than 7 W of laser radiation around 1 m was obtained under 14.4 W of incident pump power at 978 nm, leading to high optical conversions of more than 50%. Finally, both crystals demonstrate little sensitivity to pump wavelength drift and exhibit broad tunability at a multiwatt level (more than 4 W over 50 nm and 60 nm, respectively for Yb:LSO and Yb:YSO). PACS 42.55.Xi; 42.60.Pk; 42.70.Hj     

Z-scan measurements of the nonlinear refractive indices of novel Yb-doped laser crystal hosts

We report on the z-scan characterization of the nonlinear refractive indices of three borate crystals (GdCOB, YCOB, and BOYS), which are new promising Yb-doped laser hosts. The results indicate the possibility of substantial Kerr-lensing and self-phase modulation effects in femtosecond oscillators and amplifiers. High values of the nonlinear refractive indices suggest possible KLM operation of such lasers. PACS 42.65.An; 42.65.Hw; 42.55.Rz; 42.65.Re